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Glycoside Hydrolase Family 127
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|Glycoside Hydrolase Family GH127|
|Active site residues||known|
|CAZy DB link|
This family of glycoside hydrolases contains β-L-arabinofuranosidase activity, which was established for HypBA1 from Bifidobacterium longum JCM 1217 . HypBA1 released L-arabinose from the following saccharides and amino acid glycoconjugates, but not from from hydroxyproline-rich glycoproteins (HRGPs) such as carrot extensin and potato lectin:
- Arafβ1-2Araf (β-Ara2, a product of the GH121 β-L-arabinobiosidase from B. longum JCM 1217 )
- Arafβ-hydroxyproline (Ara-Hyp)
- Arafβ1-2Arafβ-Hyp (Ara2-Hyp)
- Arafβ1-2Arafβ1-2Arafβ-hyp (Ara3-Hyp)
- methyl β-L-arabinofuranoside
The members of GH127 were previosuly known as members of the Pfam DUF1680 family, which is conserved in many species of bacteria, actinomycetes, fungi, and plants. Establishment of GH127 by biochemical analysis thus resolved the "domain of unknown function" status of this PFAM family.
Note: The original paper describing B. longum HypBA1 as the founding member of GH127  was withdrawn in 2013  and a revised version was published in 2014 , to correct errors due to an inadvertent mix-up of sample tubes and data for the E338A and E366A mutants.
Kinetics and Mechanism
HypBA1 is a retaining enzyme. The stereochemical course of the reaction was shown by transglycosylation activity toward 1-alkanols, such as methanol, and produced methyl β-L-arabinofuranoside was identified by 1H-NMR and 13C-NMR analysis 
In the crystal structure of HypBA1, a Zn2+ ion was bound to the active site . A cysteine residue (Cys417), which is involved in the coordination of the Zn2+, was suggested to act as the nucleophile. Glu322 is possibly the acid/base catalyst. A possible reaction mechanism involving the cysteine residue as the nucleophile was suggested based on crystal structures, site-directed mutagenesis, some biochemical analysis, and quantum mechanical calculations .
HypBA1 from B. longum JCM 1217 . It consists of a catalytic (α/α)6 barrel domain and two additional β-sandwich domains.
- First stereochemistry determination
- This was determined with HypBA1 enzyme by measurement of glycosyl transfer reactions to methanol and the 1H-NMR and13C-NMR spectra .
- First catalytic nucleophile identification
- First general acid/base residue identification
- First 3-D structure
- HypBA1 from B. longum JCM 1217 by X-ray crystallography .
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